During recent years, increasing attention has been paid by industry and the general public in Western Europe and North America to the environmental effects of the many substances that are employed in modern life. One of the classes of substances which have hitherto been widely employed comprises chlorine and oxychlorine derivatives thereof. Such compounds have been reported to generate under appropriate circumstances carcinogenic compounds and as a result, industry is seeking alternatives or replacements for such compounds in order to allay any residual public anxiety.
An alternative class of compounds comprises peroxygen compounds, of which one sub-class of especial interest comprises peracids which contain the moiety --CO--OOH. Peracids, like hydrogen peroxide, enjoy the substantial advantage of generating oxygen, either as such or in an active form during its deployment rather than chlorine or active chlorine species upon which environmentalists currently cast doubts. Furthermore, for a range of purposes such as disinfection, oxidation and bleaching, many of which are encountered domestically, peracids are more effective in general than hydrogen peroxide.
A number of the peracids are either liquid themselves or are produced conveniently in aqueous solution. Although such compositions are particularly appropriate for the treatment of or incorporation in liquid media, they are less appropriate for the treatment of solid surfaces, and particularly non-horizontal surfaces on account of the ability of liquid compositions to flow away from the point of contact. In consequence, and in order to extend the range of applications for peracids, it would be desirable to devise peracid-containing compositions that flowed less freely.
In principle, liquid compositions can be rendered less free-flowing by the incorporation of materials which thicken the liquid or introduce structure intothe liquid. However, substances which have hitherto been effective thickeners for other liquids cannot be presumed automatically to be suitable for thickening liquid peracids or peracid solutions. This difficulty derives from the very same properties of the peracids that make them effective oxidising agents and bleaches. Interaction with thickeners during storage can result in the mutual decomposition of the peracid and the thickener, which in turn not only negates the beneficial effects of thickening, but also progressively removes the capability of the peracid to perform its desired task. It will be recognised that the problem is especially apparent in the case of peracids which are themselves either liquid or are present in solution. There is also a second important difficulty in attempting to thicken peracid solutions. The presence of the peracid and the corresponding carboxylic acid from which it can be derived, tends to significantly inhibit thickening. It is believed that the difficulty arises from interference of the peracid and/or carboxylic acid with aqueous structuring mechanisms which enable surfactants and like materials to thicken aqueous solutions. However, it will be understood that the instant invention does not depend upon the accuracy of the foregoing belief or explanation, but instead it relies upon the results actually demonstrated.
By comparison with soluble peracids, the problem can be somewhat diminished in the case of substantially insoluble solid peracids that are suspended in particulate form in aqueous media, because the peracid and the liquid constitute different physical phases that consequently minimise the extent of chemical interaction between them, and the thickening of the aqueous phase can occur with a lessened risk of interference from dissolved peracid species. European patent application No. 0 160 342 discloses that insoluble peracids can be suspended by the use of a combination of a C.sub.12 -C.sub.15, primary alcohol ethoxylate having 7 ethylene oxides, alkylbenzene sulphonate and very high levels (&gt;6% w/w) of an electrolyte such as sodium sulphate. European patent application No. 0 201 958 teaches that insoluble peracids can be suspended by a C.sub.12 -C.sub.14 alcohol ethoxylate having 7.5 ethoxylates in combination with sodium dodecylbenzene sulphonate, but that the pH of these compositions must be maintained between 3.5 and 4.1, a very narrow and restrictive pH range. European patent application No. 0 442 549 teaches that insoluble peracids can be suspended by C.sub.12 -C.sub.15 alcohol ethoxylate having 3 ethoxylates in combination with a secondary alkane sulphonate and 10% w/w sodium sulphate.
It will be understood that some other potential thickeners may initially or after a brief period of storage produce a much thickened composition, but one which is rather unstable, in that its viscosity falls away rapidly from its peak. Tests employing anionic polyacrylamides fell into that category.
It will be recognised that many applications for thickened peroxygens result in the thickened compositions being discharged into the waste water system, and therefore it is desirable that the thickeners employed should possess an acceptable degree of biodegradability, and preferably the more biodegradable the thickener the better. UK patent application No. 2,255,507 discloses that a combination of a dinonylphenol ethoxylate with an amine oxide or a mixture of a fatty alcohol ethoxylate and a polyether can be employed to thicken peracetic acid solutions. However, dinonyl phenol ethoxylates are very poorly biodegradable, and are not acceptable for discharge into drainage water in many countries. The peracetic acid compositions thickened with dinonylphenolethoxylates were also found to develop a strong yellow colouration on storage, which may be unacceptable in certain potential applications.
International patent application No. WO/9424863 discloses that certain block copolymers can be employed to thicken peracetic acid solutions in which the concentration of peracetic acid is restricted to less than 0.09% by weight. The concentration of peracid in such solutions is very low, and is unsuitable for use in applications where higher concentrations of peracetic acid are required or desired.
It is an object of the present invention to seek to identify further thickening substances which are capable of thickening aqueous compositions comprising a water soluble peracid. It is a second object of some embodiments to identify further materials capable of thickening aqueous compositions comprising a water soluble peracid and obtain thereby compositions which are relatively stable chemically and physically during storage. It is a third object of a certain embodiments of the present invention to identify further materials which can thicken aqueous compositions comprising a water soluble peracid to produce viscous compositions which can be applied for disinfecting and/or cleansing purposes to non-horizontal surfaces. It is a fourth object of selected embodiments to seek to identify further thickening substances which are capable of thickening aqueous compositions comprising a water soluble peracid, and which have acceptable biodegradability. It is a fifth objective of particular embodiments of the present invention to identify a thickening system for aqueous compositions comprising a water soluble peracid which does not require the presence of high levels of electrolyte, and/or is not restricted to very dilute peracid concentrations.